#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
int main()
{
	float score, average = 0;
	int n = 0;
	scanf("%f", &score);

	while (score >= 0)
	{
		average += score;
		n++;
		scanf("%f", &score);

	}
	if (n != 0)
		average = average / n;
         
	printf("%6.2f", average);




	return 0;
}


















